1. FIELD OF THE INVENTION
The invention concerns television systems and in particular stereoscopic television systems. The invention concerns a multichannel encoding method for encoding digitized pictures, in particular digitized stereoscopic television pictures.
2. DESCRIPTION OF THE PRIOR ART
The function of a stereoscopic television system is to render the impression of depth on a screen, for example a television screen, on the basis of a stereoscopic analysis of an observed scene. This stereoscopic analysis provides pictures for the righthand view (righthand sequence) and pictures for the lefthand view (lefthand sequence) at a video frequency of 50 Hz, for example, using two frames per picture.
Stereoscopic television systems must allow for economic and technical constraints. In particular, stereoscopic television systems must integrate into an existing environment of television systems. Thus a stereoscopic television system must be compatible with the transmission standard (the MAC standard in this instance) and the transmitted signal (compatible signal) must be displayable directly on a conventional television screen.
To meet these constraints the original righthand and lefthand picture sequences can only be transmitted in part, the untransmitted part having to be reconstituted in the decoder of the stereoscopic television receiver to obtain a stereoscopic display. To achieve a high degree of compatibility the choice may be made to transmit only one sequence of pictures (the righthand or lefthand sequence) but it is preferable to transmit a sequence of pictures resulting from the multiplexing of picture sequences (righthand and lefthand with compatible image enhancement processing) to favor stereoscopic output.
The basic reconstitution algorithm is a movement compensation algorithm applied to digitized television pictures subdivided into blocks of pixels (picture elements). This algorithm works correctly for blocks containing small or moderate movement. Blocks containing large or irregular movement are not well reconstituted, however. Consequently, for these blocks containing large or irregular movement it is necessary to use other processing channels such as a filtered channel.
Multichannel encoding methods for encoding digitized high-definition television pictures are known in which the digitized pictures are processed simultaneously in different channels including a movement estimation channel and a filtered channel. The movement estimation channel provides a movement vector for each block of pixels. A digitized picture is reconstituted for each processing channel using interpolation filters for the filtered channel and using movement vectors for the movement estimation channel. The reconstituted pictures for each block of pixels are then compared with the original picture and the processing channel which gives the best result is chosen to transmit the block in question.
However, this "a posteriori" choice of a specific processing channel following reconstitution by all the processing channels is not feasible for digitized stereoscopic television pictures. For depth display the pictures are not all reconstituted where there is a source picture and consequently the comparison of a reconstituted picture and the source picture is not able to yield a result usable to choose the best processing channel "a posteriori". This is essentially because the stereoscopic source pictures are acquired at 50 Hz whereas the display is at 100 Hz.
One object of the invention is a new multichannel encoding method for encoding digitized television pictures, in particular digitized stereoscopic television pictures, enabling an "a priori" choice of processing channel to made on the basis of one decision for each block of pixels.
Another object of the invention is a method of this kind which favors the movement estimation channel to retain good definition in the stereoscopic picture.